Portable devices such as personal digital assistants (PDAs), pocket PCs, iPhone, or smartphone have gained lots of popularity recently. With the development of VLSI technology, these types of mobile devices have become more light weight and have equipped with higher computing capability which in turn makes the multimedia applications such as video, audio, and game very popular. Audio playback on mobile devices, especially, has been even more successful as it was proven for the case of iPod. Audio playback may involve audio processing.
The term audio processing refers to the processing of audio signals. Audio signals are electrical signals that represent audio, i.e., sounds that are within the range of human hearing. Audio signals may be either digital or analog. Many different types of computing devices may utilize audio processing techniques. Examples of such computing devices include desktop computers, laptop computers, workstations, wireless communication devices, wireless mobile devices, personal digital assistants (PDAs), smartphones, iPods, MP3 players, handheld gaming units or other media players, and a wide variety of other devices, some of which were mentioned above.
One of the functions of audio processing is to perform audio compression or decompression, i.e., represent the audio signal with compressed data to reduce the size of audio files or restore original files out of the compressed data. There are many different audio coding (compression/decompression) algorithms that are in use today. Some examples of audio coding algorithms include MPEG-1 Audio Layer 3 (MP3), Advanced Audio Coding (AAC), High Efficiency AAC (HE-AAC), HE-AAC version 2 (HE-AAC v2), Windows Media Audio (WMA), WMA Pro, etc.
The audio file may have different formats depending on the audio coding algorithms used to compress the audio signals. The compressed data may sometimes be referred to as a bitstream. The bitstream (i.e., the compressed audio file, or parts of the compressed audio file) may be stored in a memory. Sometimes the bitstream is encrypted or stored in a format associated with an operating system of the computer or mobile device. To decompress the bitstream and to decrypt the bitstream (if it is encrypted) requires many computations per second.
The processor (sometimes called an application processor) which runs the application software may interact with a specialized processor. One type of specialized processor is known as a digital signal processor (DSP). The application processor may retrieve the bitstream from memory and pass it to the DSP to decrypt and/or decompress the bitstream. The application processor may also decrypt and/or decompress the bitstream. Decompressing the bitstream consumes power. Finding a technique to process the bitstream at a lower power is desired. Such a technique will help reduce the battery consumption of the audio decoding for mobile devices.